I know that on a binary planet you would have planetary eclipses (basically like a solar or lunar eclipse but with planets instead of moons).
If there also is a moon, things would be much more complicated.

With a binary planet and 1 moon you could get:

  • Double lunar
  • Lunar + solar
  • Lunar
  • Solar
  • Double solar

And with the double eclipses you basically have these factoring in:

  • Type (partial, penumbral (total but in penumbra), and total for lunar and partial, total, and annular for solar)
  • Visibility from planet (both from 1 or 1 from each)
  • Periodicity (how periodic the eclipses are - which I think would be almost or absolutely periodic in binary planets)

But would a lunar eclipse generally be visible from each planet and same for solar or would it vary a lot (taking the moon's path into consideration).

I think it would vary a lot since I think the moon would move in a figure 8 around the planets.

  • 1
    $\begingroup$ You need to specify the orbital configuration of your planets and moons. A binary planet with two large planets and then a smaller moon orbiting the common center of gravity of both larger planets is probably the most likely setup. $\endgroup$
    – Tim B
    Commented May 9, 2016 at 11:06
  • $\begingroup$ This should help you sort out the orbital path: en.wikipedia.org/wiki/Circumbinary_planet $\endgroup$
    – Separatrix
    Commented May 9, 2016 at 11:32
  • $\begingroup$ I think that this question I asked is related to yours, you just have to change up the distances and orbital periods. $\endgroup$ Commented May 9, 2016 at 14:17
  • $\begingroup$ @Separatrix So basically I take the orbital paths of planets orbiting binary stars and scale it down by thousands or even millions to get the orbital path $\endgroup$
    – Caters
    Commented May 10, 2016 at 3:36
  • $\begingroup$ @Caters, it would certainly give you somewhere to start. I doubt you'd be able to work out a figure of eight orbit but there could be a stable one in there somewhere. $\endgroup$
    – Separatrix
    Commented May 11, 2016 at 8:47

1 Answer 1


The orbital mechanics of 3 or more bodies are complicated and a lot of research has gone into finding physically possible configurations.

In our own solar system, out in the Kuiper belt, there are many pairs of objects circling each other. Most famous is Pluto and Charon for orbiting around a common center of gravity, but other pairs have been spotted with telescopes. When we recently got close-up photos of Pluto, scientists found several crater-pairs on its surface, evidence that pairing up is common out there. (The Kuiper belt is not so lonely after all!)

The way it works with the moons of Pluto is that Pluto and Charon circle each other in the center and the other moons, namely Styx, Nix, Kerberos and Hydra, circle further out.

Moons of pluto

A detail that is relevant to world-building, is that Pluto and Charon are tidally locked. That is, they each face each other with the same side all the time, like how Earth's moon always shows the same face to us:

enter image description here

So much for how the orbits work. Now how about eclipses? For a solar or lunar eclipse here on earth, you need the sun, the earth and the moon to all lie on a straight line. The special cases you describe sound like the case of 4 objects on a straight line. As far as I can see, an observer on the ground would only observe "ordinary" lunar and solar eclipses. The only special thing would be that after observing say, a solar eclipse, the observer could later read in the news that a lunar eclipse had taken place simultaneously on the other side of his planet.

  • $\begingroup$ But wouldn't a total solar eclipse darken the sky so much that if the star was blocked by the other planet, the moon and the lunar eclipse would be visible as well? $\endgroup$
    – Caters
    Commented Aug 17, 2016 at 17:32

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .